Thomas Jones rushed for 3,833 yards in three years with the Jets. / Robert Deutsch, USA TODAY Sports

by Nate Davis, USA TODAY Sports

by Nate Davis, USA TODAY Sports

For many former NFL players, living a life after football is like forever existing under the Sword of Damocles as they learn about additional data gathered on the aftereffects of concussions while watching peers like Junior Seau meet untimely demises.

Now, a growing number of retirees are lining up in an attempt to ensure future players don't endure what the current ones are going through.

Longtime running back Thomas Jones, who played 12 NFL seasons for five teams, will donate his brain to the Sports Legacy Institute so it can be studied for evidence of chronic traumatic encephalopathy (CTE), which was found in the brain of Seau and other deceased players. Currently, CTE can only be diagnosed postmortem.

Jones, who is also working on a documentary series on head injuries and other issues faced by ex-players, revealed his decision to ESPNNewYork.com's Jane McManus. He isn't sure how many concussions he suffered in a career that included nearly 3,000 touches.

"Honestly, like I couldn't give you a number because you just play with them," said Jones, who last played in 2011. "You can't know; nobody does. I think the guys counting the concussions were the ones that got knocked out.

"It's like taking a fresh, ripe apple and tapping it with your thumb over and over again."

Jones was one of the league's most physical runners in his prime and wasn't one to shy away from contact. He routinely lowered his head to deliver his own blows to defenders. That happened a lot between 2005 and 2009 when he averaged 308 carries per season for the Chicago Bears and New York Jets.

The Sports Legacy Institute told ESPNNewYork that Jones is among 600 living athletes who have decided to surrender their brains to science.

"Once you've bought everything you want, you realize there is more you want out of life," Jones says of the post-NFL years, perhaps speaking for many of his contemporaries.

He's certainly added significance to his life given the choice he's made once it's over.